Field of the Invention
The present invention relates to a method of forming a gettering layer by which a gettering layer for capturing metallic ions is formed on the back side of a semiconductor wafer formed with devices on the face side thereof.
Description of the Related Art
In a semiconductor device manufacturing process, a plurality of rectangular regions are demarcated by planned dividing lines called streets arranged in a grid pattern on the face side of a semiconductor wafer having a substantially circular disk-like shape, and devices such as ICs, LSIs, etc. are formed in the rectangular regions. The semiconductor wafer thus formed with a plurality of devices is divided along the streets, to form individual semiconductor devices. In order to achieve reductions in the size and weight of the semiconductor devices, normally, the back side of the semiconductor wafer is ground to attain a predetermined wafer thickness, prior to cutting the semiconductor wafer along the streets.
When the back side of the semiconductor wafer is ground as above-mentioned, however, a grinding strain layer about 1 μm in thickness which includes microcracks would be formed on the back side of the semiconductor wafer, and die strength of the semiconductor devices would be lowered when the wafer thickness is reduced to 100 μm or below. In order to solve such a problem, it is a common practice to subject the back-side surface of the semiconductor wafer to polishing, wet etching, dry etching or the like processing, after the back side of the semiconductor wafer is ground to attain a predetermined wafer thickness. By the polishing, etching or the like processing, the grinding strain layer formed on the back side of the semiconductor wafer is removed, whereby the die strength of the semiconductor devices is prevented from being lowered.
In a semiconductor wafer formed with a plurality of semiconductor devices having a memory function such as DRAM or flash memory, however, the removal of the grinding strain layer by polishing, wet etching, dry etching or the like processing after the back-side grinding would lower the memory function. The reason for such a problem is considered as follows. The metallic ions such as copper ion contained in the inside of the semiconductor wafer, in the semiconductor device manufacturing process, are located predominantly on the back side of the semiconductor wafer, due to the gettering effect, before the removal of the grinding strain layer on the back side of the semiconductor wafer. Upon the removal of the strain layer on the back side, however, the gettering effect is lost, so that the metallic ions such as copper ion having been contained in the inside of the semiconductor wafer are floated onto the face side where the devices are formed. The floating of the metallic ions onto the face side leads to the generation of current leak.
In order to solve such a problem, Japanese Patent Laid-open No. 2005-317846 proposes a semiconductor device manufacturing method wherein a grinding strain layer (gettering layer) including microcracks which is 0.2 μm or below in thickness is formed on the back side of a semiconductor wafer, whereby semiconductor devices with a gettering effect are manufactured without lowering the die strength of the semiconductor devices.